Boat trailer guiding devices for use in launching and retrieving boats are known. One such device is disclosed in U.S. Pat. No. 4,940,251 wherein a pivot device is actuated by a water scoop which picks up water when the boat trailer and boat are backed into the water on a boat ramp and which drains out when the boat trailer and device are removed from the water. This device would be cumbersome to use, difficult to attach and unpredictable in its employment. Also, there is no means for signaling the depth of water surrounding the boat trailer on the boat ramp so it would almost invite possible damage when loading large boats in an inadequate depth of water.
Another device is shown in U.S. Pat. No. 5,097,250 which discloses a rather complicated electronic system which includes a hitch sensor and sending device, a water sensor and sending device, a pair of tilt sensors and signal sending devices and a flotation sender and sending device, all coupled into a control box panel in the cab of the towing vehicle.
Other trailer marking devices are shown in U.S. Pat. No. 3,064,617 and U.S. Pat. No. 3,863,594. The boat trailer marking device of this invention offers many advantages over those shown in the prior art.